Exhaust emission control device

Abstract

To suppress deterioration of activity of a three-way catalyst during stop of fuel supply to an engine and promote combustion of soot in a filter.SOLUTION: An exhaust emission control device includes: a fuel injection valve 5; an exhaust passage 30; intake and exhaust S-VT 11, 12 for performing opening / closing control of an intake valve 21 and an exhaust valve 22; a three-way catalyst 32 disposed in an exhaust passage; a filter 33 that is disposed downstream of the three-way catalyst and on which a catalyst including an OSC material is supported; a secondary air supply passage 40 connected to the exhaust passage between the three-way catalyst and the filter; a secondary air supply device 41 for supplying secondary air to the secondary air supply passage; a secondary air control valve 42 disposed in the secondary air supply passage to control the secondary air; and an ECU 100. When decelerating an engine, the ECU controls the fuel injection valve to stop fuel supply, controls the intake and exhaust S-VT to close at least one of the intake valve and the exhaust valve, and controls the secondary air control valve to supply the secondary air periodically.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed herein relates to an exhaust gas purification device. [Background technology]

[0002] Engine exhaust gas contains harmful components such as HC (hydrocarbons), CO (carbon monoxide), NOx (nitrogen oxides), soot, etc. To prevent these harmful components from being emitted to the outside, a three-way catalyst for purifying HC, CO, and NOx, and a filter carrying a catalyst for burning and removing soot are placed in the exhaust path.

[0003] When the fuel supply to the combustion chamber is stopped during deceleration, O2 flows into the exhaust path. When the O2 oxidizes the catalytic metals contained in the three-way catalyst, such as Rh (rhodium) and Pd (palladium), the activity of the three-way catalyst decreases, its purification function deteriorates, and NOx becomes more likely to be emitted. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-60137 Summary of the Invention [Problem to be solved by the invention]

[0005] To address the above problem, one method is to close the intake or exhaust valve of the engine to prevent O2 from flowing into the exhaust path. However, if O2 is prevented from flowing into the exhaust path, O2 will no longer be supplied to the catalyst supported on the filter, which will prevent soot from being burned.

[0006] Incidentally, Patent Document 1 discloses that particulate matter on a filter is burned by supplying secondary air upstream of the filter. However, if secondary air is continuously supplied, the exhaust gas temperature and therefore the catalyst temperature will decrease, and soot will not be sufficiently burned and removed in the filter.

[0007] The technology disclosed herein has been developed in consideration of these points, and its purpose is to simultaneously prevent O2 from flowing into the three-way catalyst when fuel supply to the combustion chamber is stopped, thereby suppressing a decrease in the activity of the three-way catalyst, and to appropriately supply O2 to the filter to promote soot combustion. [Means for solving the problem]

[0008] As a result of extensive research, the inventors of the present application have discovered that by closing at least one of the intake valve and exhaust valve when the engine is decelerating and periodically supplying secondary air between the three-way catalyst and the filter, the activity of the three-way catalyst can be maintained, the filter temperature can be kept high, and soot combustion can be promoted.

[0009] Specifically, the technology disclosed here is a fuel injection valve that supplies fuel to a combustion chamber of the engine; an exhaust passage connected to a combustion chamber of the engine; a valve control device that controls the opening and closing of an intake valve that supplies air into a combustion chamber of the engine and an exhaust valve that discharges exhaust gas from the combustion chamber to the exhaust passage; a three-way catalyst disposed in the exhaust passage; a filter that is disposed downstream of the three-way catalyst in the exhaust passage, is capable of capturing particulates in the exhaust gas, and supports a catalyst containing an OSC material; a secondary air supply passage connected to the exhaust passage between the three-way catalyst and the filter; a secondary air supply device that supplies secondary air to the secondary air supply passage; a secondary air control valve disposed in the secondary air supply passage and providing periodicity to the secondary air; a controller electrically connected to the fuel injection valve, the valve control device, and the secondary air control valve, When decelerating the engine, the controller controls the fuel injection valve to stop the supply of fuel, controls the valve control device to close at least one of the intake valve and the exhaust valve, and controls the secondary air control valve to periodically supply secondary air.

[0010] According to this configuration, when the engine is decelerated, at least one of the intake valve and the exhaust valve is closed, thereby preventing O2 from flowing from the combustion chamber into the three-way catalyst, and O2 can be supplied to the filter by the secondary air supply device. This prevents the catalytic metal of the three-way catalyst from being exposed to O2 and being oxidized, making it possible to suppress a decrease in activity. In addition, supplying O2 to the catalyst supported on the filter promotes the combustion of soot in the filter.

[0011] Incidentally, catalysts used to purify exhaust gases include oxygen storage materials (OSC materials) that have the ability to absorb and release oxygen. When the air-fuel ratio of exhaust gases is leaner than the stoichiometric air-fuel ratio, such exhaust purification catalysts generate adsorption heat by adsorbing O2. When the air-fuel ratio of exhaust gases is non-lean, they generate oxidation heat by oxidizing HC and CO using the adsorbed O2. In this way, exhaust purification catalysts are characterized by repeating adsorption and oxidation reactions in a cycle of lean and non-lean states. When secondary air is steadily supplied to the exhaust purification catalyst, the catalyst always remains lean, preventing the cycle of lean and non-lean states from occurring, lowering the catalyst temperature and causing a decrease in its activity.

[0012] According to this configuration, the controller controls the secondary air control valve to periodically generate secondary air. The periodic secondary air can create the cycle of lean and non-lean states described above. The periodic secondary air generates cycles of adsorption heat and oxidation heat in the catalyst supported on the filter, allowing the catalyst to be maintained at a high temperature and promote combustion.

[0013] Further, a temperature detection means for detecting the temperature of the three-way catalyst or the filter is provided, The controller may be electrically connected to the temperature detection means, determine whether the temperature detected by the temperature detection means is equal to or higher than a predetermined judgment temperature, and control the secondary air control valve to periodically supply secondary air when the temperature detected by the temperature detection means is equal to or higher than the judgment temperature and the engine is decelerating.

[0014] According to this configuration, when the temperature of the three-way catalyst or the catalyst supported on the filter is above a predetermined judgment temperature and the engine is decelerating, periodic supply of secondary air is performed, thereby promoting the combustion of soot in the filter.

[0015] Further, when the temperature detected by the temperature detection means is lower than the judgment temperature, the secondary air control valve may be controlled to periodically supply secondary air.

[0016] According to this configuration, when the temperature of the three-way catalyst or the catalyst supported on the filter is below a predetermined judgment temperature, secondary air is periodically supplied regardless of whether the engine is decelerating or not, thereby preventing a decrease in activity due to a drop in catalyst temperature.

[0017] In one embodiment, the controller may control the secondary air control valve to supply secondary air having a predetermined frequency and maximum amplitude of oxygen concentration, and the secondary air control valve may be configured to set the maximum amplitude of oxygen concentration to be greater than 0.50% and not greater than 3.0% when the frequency of the secondary air is set to a fixed value greater than 0 Hz and not greater than 1.5 Hz.

[0018] This configuration makes it possible to enhance the effect of purifying at least HC, one of the harmful components contained in exhaust gas, in the catalyst supported on the filter. Specifically, it is possible to lower the gas temperature at the catalyst inlet when the HC purification rate reaches 50% (T50(HC)).

[0019] It is preferable that the secondary air control valve controls the maximum amplitude of the oxygen concentration of the secondary air to be greater than 0.66% and not more than 3.0%.

[0020] This configuration makes it possible to improve the effectiveness of the catalyst supported on the filter in purifying HC and CO, among the harmful components contained in exhaust gas. Specifically, it is possible to lower T50(HC) and also to lower the gas temperature at the catalyst inlet when the CO purification rate reaches 50% (T50(CO)).

[0021] More preferably, the secondary air control valve controls the maximum amplitude of the oxygen concentration of the secondary air to be 0.78% or more and 2.2% or less.

[0022] This configuration makes it possible to further enhance the effect of purifying HC and CO, among the harmful components contained in exhaust gas, in the catalyst supported on the filter. Specifically, it is possible to reduce T50(HC) by 9°C or more, and T50(CO) by 5°C or more.

[0023] In one embodiment, the controller may control the secondary air control valve to supply secondary air having a predetermined vibration frequency and maximum amplitude of oxygen concentration, and the secondary air control valve may be configured to set the vibration frequency to greater than 0 Hz and less than or equal to 1.5 Hz when the maximum amplitude of the oxygen concentration of the secondary air is set to a fixed value greater than 0% and less than or equal to 3.0%.

[0024] This configuration makes it possible to enhance the effect of purifying at least HC, among the harmful components contained in exhaust gas, in the catalyst supported on the filter. Specifically, it is possible to reduce T50(HC).

[0025] The secondary air control valve preferably controls the frequency of the secondary air to be 0.20 Hz or more and 0.94 Hz or less, or 1.2 Hz or more and 1.5 Hz or less.

[0026] This configuration makes it possible to further enhance the effect of purifying HC, one of the harmful components contained in exhaust gas, in the catalyst supported on the filter. Specifically, it is possible to reduce T50(HC) by 5°C or more.

[0027] More preferably, the secondary air control valve controls the frequency of the secondary air to be greater than 0.25 Hz and less than 0.82 Hz.

[0028] This configuration makes it possible to enhance the effect of purifying HC and CO, among the harmful components contained in exhaust gas, in the catalyst supported on the filter. Specifically, it is possible to reduce T50(HC) by 7°C or more, and also reduce T50(CO). [Effects of the Invention]

[0029] As described above, the exhaust purification device disclosed herein can simultaneously prevent O2 from flowing into the three-way catalyst to suppress a decrease in the activity of the three-way catalyst when fuel supply to the combustion chamber is stopped, and appropriately supply O2 to the filter to promote soot combustion. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 is a schematic diagram illustrating an engine system to which an exhaust purification device is applied. [Figure 2] FIG. 2 is a block diagram of an engine system to which the exhaust purification device is applied. [Figure 3] FIG. 3 is a flowchart illustrating a control procedure for controlling the exhaust purification device, which is executed by the ECU. [Figure 4] FIG. 4 is a graph showing T50 when the frequency of the secondary air is fixed at a predetermined value and the maximum oxygen concentration is changed. [Figure 5] FIG. 5 is a graph showing T50 when the frequency of secondary air is fixed at a predetermined value and the maximum oxygen concentration is changed. [Figure 6]FIG. 6 is a graph showing T50 when the maximum oxygen concentration of the secondary air is fixed at a predetermined value and the vibration frequency is changed. [Figure 7] FIG. 7 is a graph showing T50 when the maximum oxygen concentration of the secondary air is fixed at a predetermined value and the vibration frequency is changed. DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, an embodiment of an engine system to which an exhaust gas purification device is applied will be described with reference to the drawings. The exhaust gas purification device described here is an example.

[0032] Fig. 1 is a schematic diagram illustrating an engine system to which an exhaust gas purification device is applied, and Fig. 2 is a block diagram illustrating an engine system to which an exhaust gas purification device is applied.

[0033] The engine system has an engine 1. The engine 1 is mounted on a four-wheeled automobile. The automobile runs when the engine 1 is driven. The fuel for the engine 1 is gasoline in this configuration example.

[0034] (Engine configuration) Engine 1 has a cylinder 2 and a piston 3 inserted into cylinder 2. The piston 3 reciprocates due to combustion of an air-fuel mixture in a combustion chamber 4 inside cylinder 2, and an intake stroke, compression stroke, expansion stroke, and exhaust stroke are repeated within cylinder 2. Engine 1 has a fuel injection valve 5 that supplies fuel to combustion chamber 4, and an intake passage 20 and an exhaust passage 30 that are connected to combustion chamber 4. Air supplied from intake passage 20 is introduced into combustion chamber 4 by an intake valve 21. Exhaust gas generated by combustion of the air-fuel mixture in combustion chamber 4 is discharged into exhaust passage 30 by an exhaust valve 31.

[0035] The intake valve 21 and the exhaust valve 31 are controlled to open and close by a valve control device. The valve control device adjusts the amount of air introduced into the cylinder 2 and the amount of burned gas introduced into the cylinder 2 by controlling the opening and closing of the intake valve 21 or the exhaust valve 31. When the supply of fuel to the combustion chamber 4 is stopped during engine deceleration, as described below, the valve control device closes at least one of the intake valve 21 or the exhaust valve 31. The valve control device is a variable valve mechanism that varies the valve timing and / or valve lift, and as shown in FIG. 2, is, for example, an electric or hydraulic intake S-VT (Sequential-Valve Timing) 11 and exhaust S-VT 12. The intake S-VT 11 and exhaust S-VT 12 continuously change the rotational phase of the intake camshaft and the exhaust camshaft, respectively, within a predetermined angle range.

[0036] A throttle valve 23 that adjusts the amount of intake air passing through is disposed upstream of the intake passage 20, and an air cleaner 25 is disposed further upstream of the throttle valve 23. The throttle valve 23 is electrically operated based on a required fuel injection amount based on the accelerator opening degree of the driver and a command signal from the ECU 10, which will be described later. The opening degree of the throttle valve 23 is detected by a throttle opening degree sensor SW4. The air cleaner 25 filters the air.

[0037] (exhaust gas purification catalyst) A three-way catalyst 32 for purifying exhaust gas is disposed downstream of the exhaust passage 30. The three-way catalyst 32 is an exhaust purification catalyst that activates at a predetermined temperature or higher and purifies harmful substances in the exhaust gas, primarily nitrogen oxides (NOx), by reducing them and oxidizing hydrocarbons (HC) and carbon monoxide (CO). Specifically, the three-way catalyst 32 has a catalytic layer formed inside a cylindrical case. The catalytic layer is formed, for example, on a carrier, supporting precious metal particles such as Rh (rhodium), Pd (palladium), and Pt (platinum), as well as an OSC material or other promoter. The three-way catalyst 32 enhances the NOx purification rate when the exhaust gas has a rich air-fuel ratio (A / F). When the three-way catalyst 32 is exposed to oxygen, the supported catalytic metal oxidizes, reducing its activity and resulting in a lower NOx purification rate. The three-way catalyst 32 has an OSC (Oxygen Storage Capacity) function. A catalyst temperature sensor SW1 capable of detecting the temperature of exhaust gas passing near the inlet of the three-way catalyst 32 is disposed upstream of the three-way catalyst 32. The temperature of the three-way catalyst 32 can be estimated from the temperature detected by the catalyst temperature sensor SW1. The catalyst temperature sensor SW1 corresponds to the "catalyst temperature detection means" in the claims. The catalyst temperature sensor SW1 may be disposed near the inlet of the filter 33 and be capable of estimating the temperature of the filter 33.

[0038] A filter 33 is disposed in the exhaust passage 30 downstream of the three-way catalyst 32. The filter 33 is capable of capturing particulate matter such as soot in the exhaust gas and supports an exhaust purification catalyst capable of combusting the captured particulate matter. The main body of the filter 33 is formed of an inorganic porous material such as cordierite, SiC, Si3N4, sialon, or AlTiO3. The catalyst supported by the filter 33 includes an OSC material, such as a Pt-supported catalyst on activated alumina or a mixture of a Zr-based composite oxide and a Rh-doped Ce-containing Zr-based composite oxide. Ce-containing oxides can function as the OSC material. The OSC material generates adsorption heat by adsorbing O2 when the exhaust gas air-fuel ratio is leaner than the stoichiometric air-fuel ratio. When the exhaust gas air-fuel ratio is not lean, the OSC material generates oxidation heat by oxidizing HC and CO using the adsorbed O2. The filter 33 is, for example, a gasoline particulate filter (GPF).

[0039] (Secondary air supply type) A secondary air supply passage 40 is connected to the exhaust passage 30 between the three-way catalyst 32 and the filter 33. Secondary air is supplied to the secondary air supply passage 40 from a secondary air supply device 41. The secondary air supply device 41 is, for example, an air pump that sends outside air into the secondary air supply passage 40. The secondary air is not limited to outside air, and may be air supplied from the intake passage or the exhaust passage by providing a branch passage in the intake passage or the exhaust passage. A secondary air control valve 42 is disposed in the secondary air supply passage 40 between the secondary air supply device 41 and the exhaust passage 30. The secondary air control valve 42 imparts periodicity to the secondary air supplied from the secondary air supply device 41. Specifically, the secondary air control valve 42 controls the flow rate of the secondary air to change periodically by opening and closing the valve. The secondary air has an amplitude and a frequency set by the secondary air control valve 42 and is periodically supplied to the exhaust passage 30. The amplitude here refers to the maximum concentration of secondary air introduced (maximum amplitude [%] of oxygen concentration) (hereinafter also simply referred to as "amplitude"). By periodically supplying secondary air to the exhaust passage 30, it is possible to lower T50, which is the gas temperature at the catalyst inlet when the HC purification rate and CO purification rate in the exhaust purification catalyst reach 50%.

[0040] (Amplitude and frequency of secondary air) The amplitude and frequency of the secondary air can be set arbitrarily by the secondary air control valve 42, and the amplitude and frequency may be maintained at a constant cycle or may be varied. Incidentally, when the exhaust gas air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the exhaust purification catalyst generates heat of adsorption by adsorbing O2, and when the exhaust gas air-fuel ratio is non-lean, it generates heat of oxidation by oxidizing HC and CO using the adsorbed O2. Thus, the catalyst supported on the filter has the characteristic of cycling between lean and non-lean states. Periodic secondary air can create a cycle of lean and non-lean states, and supplying such secondary air creates a cycle of heat of adsorption and oxidation in the exhaust purification catalyst supported on the filter, making it possible to maintain a high temperature and promote combustion.

[0041] From the viewpoint of energy efficiency relative to the output of the air pump 41, the amplitude of the secondary air is preferably 3% or less. By increasing the amplitude to more than 0.5%, the gas temperature (T50(HC)) at the catalyst inlet when the HC purification rate reaches at least 50% is lower than when no secondary air is supplied (amplitude 0%), thereby improving HC purification performance. By increasing the amplitude to more than 0.66%, T50(HC) and T50(CO) are lowered, thereby improving HC and CO purification performance. By setting the amplitude to 0.70 or more, T50(HC) is lowered by at least 5°C or more, thereby significantly improving HC purification performance. By setting the amplitude to 0.78 or more and 2.2 or less, T50(HC) and T50(CO) are lowered by 5°C or more, thereby significantly improving HC and CO purification performance.

[0042] By setting the frequency of the secondary air to a value within a predetermined range, it is possible to supply secondary air at a cycle close to the above-described O2 adsorption and release cycle speed specific to the exhaust purification catalyst, which is thought to activate the catalytic reaction. The frequency is preferably 1.5 Hz or less. Furthermore, by setting the frequency higher than 0 Hz, it is possible to reduce T50(HC) at least compared to a state in which secondary air is not supplied (frequency of 0 Hz), thereby improving HC purification performance. By setting the frequency to 0.20 Hz or higher and 0.94 Hz or lower, or 1.2 Hz or higher and 1.5 Hz or lower, it is possible to reduce T50(HC) by at least 5°C or more, thereby significantly improving HC purification performance. By setting the frequency to be higher than 0.25 Hz but lower than 0.82 Hz, it is possible to reduce T50(HC) and T50(CO), thereby improving HC and CO purification performance.

[0043] (Control system) Next, a control system of the exhaust purification device will be described with reference to Fig. 2. The engine system of this embodiment is controlled by an ECU (Engine Control Unit) 100 provided in a vehicle. The ECU 100 is a controller based on a well-known microcomputer, and includes a central processing unit (CPU) 101, a memory 102, and an I / F circuit 103. The CPU 101 executes programs. The memory 102 is configured, for example, by a RAM (Random Access Memory) or a ROM (Read Only Memory), and stores programs and data. The I / F circuit 103 inputs and outputs electrical signals. The ECU 10 is an example of a controller.

[0044] 1 and 2, various sensors SW1 to SW4 are electrically connected to the ECU 100. The sensors SW1 to SW4 output signals to the ECU 100. The sensors include the following sensors. Catalyst temperature sensor SW1: disposed upstream of the three-way catalyst 32 in the exhaust passage 30, and detects the temperature of the air flowing through the exhaust passage 30. Accelerator opening sensor SW2: Attached to the accelerator pedal mechanism, it detects the amount of accelerator pedal depression (accelerator opening). Engine revolution speed sensor SW3: attached to engine 1 and detects the revolution speed of engine 1. Throttle opening sensor SW4: attached to the throttle valve 23 and detects the opening of the throttle valve 23.

[0045] The ECU 100 determines the operating state of the engine 1 based on signals from sensors SW1 to SW4, etc., and calculates the control amount of each device according to a predetermined control logic. The control logic is stored in a memory 102. The control logic includes calculating a target amount and / or a control amount using a map stored in the memory 102.

[0046] The ECU 100 is electrically connected to devices such as the fuel injector 5, intake S-VT 11, exhaust S-VT 12, throttle valve 23, secondary air supply device 41, and secondary air control valve 42. The ECU 100 outputs electrical signals related to the calculated control amount to the fuel injector 5, intake S-VT 11, exhaust S-VT 12, throttle valve 23, secondary air supply device 41, and secondary air control valve 42.

[0047] (Control when catalyst temperature drops) As a controller for the exhaust purification device, ECU 100 supplies secondary air to the exhaust purification catalyst when the temperature of the exhaust purification catalyst drops to activate it. Specifically, ECU 100 determines whether the temperature detected by catalyst temperature sensor SW1 is equal to or higher than a predetermined judgment temperature stored in memory 102, and if the temperature is lower than the predetermined judgment temperature, it outputs a control signal to secondary air supply device 41 and secondary air control valve 42 to periodically supply secondary air from secondary air supply passage 40 to exhaust passage 30. In this way, the periodic supply of secondary air to filter 33 generates a cycle of adsorption heat and oxidation heat, which keeps the catalyst temperature high and promotes combustion function. The predetermined judgment temperature is a temperature range in which the exhaust purification catalyst can exert its purification effect, for example, between 200°C and 400°C.

[0048] (Control during deceleration fuel cut) As a controller of the exhaust purification device, when decelerating the engine 1, the ECU 100 stops the supply of fuel to the combustion chamber 4, closes at least one of the intake valve 21 and the exhaust valve 31, and supplies secondary air in the same manner as when the catalyst temperature drops. Specifically, when the engine 1 is decelerating and a predetermined deceleration fuel cut condition is met, the ECU 100 controls the fuel injection valve 5 to stop the supply of fuel to the combustion chamber 4, thereby performing deceleration fuel cut. The deceleration fuel cut condition is, for example, a condition in which the throttle valve 23 determined by the throttle opening sensor SW4 is fully closed and the rotation speed of the engine 1 determined by the engine speed sensor SW3 is higher than a predetermined rotation speed (a rotation speed slightly higher than the idle rotation speed). During deceleration fuel cut, the ECU 100 sends a control signal to at least one of the intake S-VT 11 and the exhaust S-VT 12 to close at least one of the intake valve 21 and the exhaust valve 31. Furthermore, during deceleration fuel cutoff, a control signal is output to the secondary air supply device 41 and the secondary air control valve 42, and secondary air is periodically supplied from the secondary air supply passage 40 to the exhaust passage 30. In this way, closing at least one of the intake valve 21 and the exhaust valve 31 during deceleration fuel cutoff prevents O2 from flowing from the combustion chamber into the three-way catalyst, preventing the catalytic metal from being exposed to O2 and being oxidized, and supplying secondary air to the filter 33 promotes the combustion of soot carried on the filter.

[0049] During deceleration fuel cut, it is preferable that the ECU 100 closes the intake valve 21 and opens the exhaust valve 31, and controls the fuel injection valve 5 and the like so that the air-fuel ratio in the combustion chamber 4 is slightly richer (λ<1) than the stoichiometric air-fuel ratio (A / F=14.7) (λ=1), for example, approximately A / F=14. This prevents oxygen from flowing from the combustion chamber 4 into the exhaust passage 30 and allows a certain amount of fuel to flow into the three-way catalyst 32, thereby continuing the catalytic reaction of the three-way catalyst 32 and maintaining a high temperature. Note that the air-fuel ratio is not limited to this, and may be the stoichiometric air-fuel ratio.

[0050] Next, a control procedure of the exhaust purification device executed by the ECU 100 will be described with reference to Fig. 3. First, in step S1, the ECU 100 injects fuel into the combustion chamber using the fuel injection valve 5 and ignites the fuel using the ignition device to start the engine 1.

[0051] In step S2, ECU 100 determines whether the temperature detected by catalyst temperature sensor SW1 is equal to or higher than a predetermined judgment temperature stored in memory 102. If the temperature detected by catalyst temperature sensor SW1 is equal to or higher than the predetermined judgment temperature (YES in step S2), ECU 100 proceeds to step S3. If the temperature detected by catalyst temperature sensor SW1 is not equal to or higher than the predetermined judgment temperature (NO in step S2), ECU 100 proceeds to step S5.

[0052] In step S3, the ECU 100 reads information from the throttle opening sensor SW4 and the engine speed sensor SW3 and determines whether or not the deceleration fuel cut condition is met. If the determination in step S3 is YES, the process proceeds to step S4.

[0053] In step S4, the ECU 100 transmits a control signal to at least one of the intake S-VT 11 and the exhaust S-VT 12 to close at least one of the intake valve 21 and the exhaust valve 31, and then proceeds to step S5.

[0054] In step S5, the ECU 100 outputs control signals to the secondary air supply device 41 and the secondary air control valve 42, and periodically supplies secondary air from the secondary air supply passage 40 to the exhaust passage 30.

[0055] In step S6, the ECU 100 reads information from various sensors, and when the operation of the engine 1 is stopped, the process proceeds to step S7. While the engine 1 is operating, the ECU 100 continues to monitor the catalyst temperature using the catalyst temperature sensor SW1 in step S2.

[0056] In step S7, the ECU 100 outputs control signals to the secondary air supply device 41 and the secondary air control valve 42 to stop the supply of secondary air to the exhaust passage 30.

[0057] 3, when the temperature of the exhaust purification catalyst drops, ECU 100 activates the exhaust purification catalyst by supplying secondary air to the exhaust purification catalyst regardless of whether the engine is in a deceleration fuel cut state. Also, when the temperature of the exhaust purification catalyst is appropriate, ECU 100 closes at least one of intake valve 21 and exhaust valve 31 and supplies secondary air only when the engine is in a deceleration fuel cut state, thereby preventing oxidation of the three-way catalyst and promoting the combustion of soot in the filter. In either case, it is possible to suppress a drop in the temperature of the exhaust purification catalyst and maintain high activity.

[0058] (Experimental example) Next, a specific example of an experiment that was carried out will be described. The following experiment was carried out to verify that catalytic activity can be improved by periodically supplying secondary air to an exhaust purification catalyst.

[0059] The exhaust purification catalyst used a mixture of rhodium and palladium as precious metal particles, cerium-zirconium composite oxide and alumina as promoters, and zirconia as a binder. The substrate material was cordierite, and a flow-through type was used.

[0060] (Evaluation conditions) The base gas composition is 0.77%-O2, 0.9%-CO, 400 ppm-NO, 600 ppmC-C3H6, 100 ppmC-C2H4, 800 ppmC-normal C8H 18 , 10%-H2O. To this base gas, O2 of a predetermined concentration and frequency, simulating secondary air, was added to create a simulated gas for testing. The simulated gas flow was controlled so that the space velocity was 36,000 (1 / h) and the temperature was raised to 600°C at a rate of 30°C / min.

[0061] The gas temperature at the catalyst inlet when the HC conversion rate reaches 50% (T50(HC)) and the gas temperature at the catalyst inlet when the CO conversion rate reaches 50% (T50(CO)) are shown in Figures 4 to 7 and Tables 1 to 4.

[0062] [Table 1]

[0063] [Table 2]

[0064] [Table 3]

[0065] [Table 4]

[0066] (Evaluation result 1) The results are shown in Figure 4 and Table 1, where the frequency was fixed at 0.25 Hz and the amplitude was set to a predetermined value between 0% and 3.0%. According to the figure, when the amplitude was greater than 0% and not more than 3%, T50(HC) was lower than the state where no simulated gas was supplied (T50(HC) at 0% amplitude), as indicated by the dashed line in the figure, demonstrating an improvement in catalytic activity against HC. Note that when the amplitude was 0.42% or greater, T50(HC) was lower by 5°C or more than the state where no simulated gas was supplied (T50(HC) at 0% amplitude), as indicated by the dashed line in the figure, demonstrating a further improvement in activity within this range. In addition, T When the amplitude was greater than 0.30% and less than or equal to 3.0%, T50(CO) was lower than the state where no simulant gas was supplied (T50(CO) at 0% amplitude), as indicated by the dashed line in the figure, demonstrating improved catalytic activity for CO. Furthermore, when the amplitude was greater than or equal to 0.62% and less than or equal to 1.8%, T50(CO) was lower by 5°C or more than the state where no simulant gas was supplied (T50(CO) at 0% amplitude), as indicated by the dashed line in the figure, demonstrating further improved activity in this range.

[0067] (Evaluation result 2) The results for a fixed frequency of 0.5 Hz and a predetermined amplitude ranging from 0% to 3.0% are shown in Figure 5 and Table 2. According to the figure, when the amplitude was greater than 0.50% and less than or equal to 3.0%, T50(HC) was lower than the T50(HC) at 0% amplitude (shown by the dashed line in the figure), demonstrating improved catalytic activity toward HC. Furthermore, when the amplitude was greater than 0.70%, T50(HC) was lower by 5°C or more than the T50(HC) at 0% amplitude (shown by the dashed line in the figure), demonstrating further improvement in activity within this range. Furthermore, when the amplitude was greater than 0.66% and less than or equal to 3.0%, T50(CO) was lower than the T50(CO) at 0% amplitude (shown by the dashed line in the figure), demonstrating improved catalytic activity toward CO. In addition, when the amplitude is between 0.78% and 2.2%, T50(CO) is lower by 5°C or more than T50(CO) at an amplitude of 0%, as shown by the dashed line in the figure, and further improvement in activity was observed in this range.

[0068] Evaluation results 1 and 2 revealed a more appropriate amplitude range for the secondary air. When the vibration frequency was fixed at a value greater than 0 Hz and less than or equal to 1.5 Hz, increasing the amplitude to more than 0.50% reduced at least T50(HC). Increasing the amplitude to more than 0.66% reduced both T50(HC) and T50(CO). Increasing the amplitude to 0.7 or more reduced T50(HC) by 5°C or more, significantly improving HC purification performance. Increasing the amplitude to 0.78 to 2.2 reduced T50(HC) by 9°C or more and T50(CO) by 5°C or more, significantly improving HC and CO purification performance.

[0069] (Evaluation result 3) The results for a fixed amplitude of 1.0% and a frequency of 0 to 1.5 Hz are shown in Figure 6 and Table 3. As shown in Figure 6, when the frequency was greater than 0 Hz and less than or equal to 1.5 Hz, T50(HC) was lower than the T50(HC) at a frequency of 0 Hz, indicated by the dashed line in the figure, demonstrating improved catalytic activity toward HC. Furthermore, when the frequency was between 0.16 and 0.94 Hz or between 1.2 and 1.5 Hz, T50(HC) was lower by 5°C or more than the T50(HC) at a frequency of 0 Hz, indicated by the dashed line in the figure, demonstrating further improvement in activity within these ranges. Furthermore, when the frequency was greater than 0.14 Hz and less than or equal to 1.5 Hz, T50(CO) was lower than the T50(CO) at an amplitude of 0%, indicated by the dashed line in the figure, demonstrating improved catalytic activity toward CO. In addition, when the frequency was between 0.22 Hz and 0.78 Hz, T50(CO) was 5°C or more lower than T50(CO) at 0% amplitude, as shown by the dashed line in the figure, and further improvement in activity was observed in this range.

[0070] (Evaluation result 4) The results for a fixed amplitude of 2.0% and a frequency of 0 to 1.5 Hz are shown in Figure 7 and Table 4. According to the figure, when the frequency was greater than 0 Hz and less than or equal to 1.5 Hz, T50(HC) was lower than the T50(HC) at a frequency of 0 Hz, as shown by the dashed line in the figure, demonstrating improved catalytic activity toward HC. Furthermore, when the frequency was greater than 0.20 Hz and less than or equal to 1.5 Hz, T50(HC) was lower by 5°C or more than the T50(HC) at a frequency of 0 Hz, as shown by the dashed line in the figure, demonstrating further improvement in activity within this range. Furthermore, when the frequency was greater than 0.25 Hz and less than or equal to 0.82 Hz, T50(CO) was lower than the T50(CO) at an amplitude of 0%, as shown by the dashed line in the figure, demonstrating improved catalytic activity toward CO.

[0071] Evaluation results 3 and 4 revealed a more appropriate frequency range for the secondary air. When the amplitude is set to a fixed value greater than 0% and less than 3.0%, increasing the frequency above 0 Hz reduces at least T50(HC) and improves HC purification performance. By setting the frequency to greater than 0.20 Hz and less than 0.94 Hz or 1.2 Hz to 1.5 Hz, T50(HC) can be reduced by at least 5°C, significantly improving HC purification performance. By setting the frequency to greater than 0.25 Hz and less than 0.82 Hz, T50(HC) can be reduced by 7°C or more, and T50(CO) can also be reduced, improving HC and CO purification performance. [Explanation of symbols]

[0072] 1 engine 4 Combustion chamber 10 ECU (controller) 11 Intake S-VT (valve control device) 12 Exhaust S-VT (valve control device) 20 Intake passage 21 Intake valve 30 Exhaust passage 31 Exhaust valve 32 Three-way catalyst 33 Filters 40 Secondary air supply passage 41 Air pump (secondary air supply device) 42 Secondary air control valve 100 ECU (Controller) SW1 Catalyst temperature sensor (temperature detection means)

Claims

1. a fuel injection valve that supplies fuel to a combustion chamber of the engine; an exhaust passage connected to a combustion chamber of the engine; a valve control device that controls the opening and closing of an intake valve that introduces air into a combustion chamber of the engine and an exhaust valve that discharges exhaust gas from the combustion chamber to the exhaust passage; a three-way catalyst disposed in the exhaust passage; a filter that is disposed downstream of the three-way catalyst in the exhaust passage, capable of capturing particulates in the exhaust gas, and that supports a catalyst containing an OSC material; a secondary air supply passage connected to the exhaust passage between the three-way catalyst and the filter; a secondary air supply device that supplies secondary air to the secondary air supply passage; a secondary air control valve disposed in the secondary air supply passage and providing periodicity to the secondary air; a controller electrically connected to the fuel injection valve, the valve control device, and the secondary air control valve, When decelerating the engine, the controller controls the fuel injection valve to stop the supply of fuel, controls the valve control device to close at least one of the intake valve and the exhaust valve, and controls the secondary air control valve to periodically supply secondary air. An exhaust gas purification device characterized by:

2. The exhaust gas purification device according to claim 1, a temperature detection means for detecting the temperature of the three-way catalyst or the filter; the controller is electrically connected to the temperature detection means, and determines whether the temperature detected by the temperature detection means is equal to or higher than a predetermined judgment temperature, and when the temperature detected by the temperature detection means is equal to or higher than the judgment temperature and the engine is decelerating, controls the secondary air control valve to periodically supply secondary air. An exhaust gas purification device characterized by:

3. The exhaust gas purification device according to claim 2, When the temperature detected by the temperature detection means is lower than the judgment temperature, the secondary air control valve is controlled to periodically supply secondary air. An exhaust gas purification device characterized by:

4. The exhaust gas purification device according to claim 3, the controller controls the secondary air control valve to supply secondary air having a predetermined frequency and maximum amplitude of oxygen concentration, and the secondary air control valve sets the maximum amplitude of oxygen concentration to be greater than 0.50% and not greater than 3.0% when the frequency of the secondary air is set to a fixed value greater than 0 Hz and not greater than 1.5 Hz. An exhaust gas purification device characterized by:

5. The exhaust gas purification device according to claim 4, The secondary air control valve controls the maximum amplitude of the oxygen concentration of the secondary air to be greater than 0.66% and not greater than 3.0%. An exhaust gas purification device characterized by:

6. The exhaust gas purification device according to claim 5, The secondary air control valve controls the maximum amplitude of the oxygen concentration of the secondary air to be 0.78% or more and 2.2% or less. An exhaust gas purification device characterized by:

7. The exhaust gas purification device according to claim 3, the controller controls the secondary air control valve to supply secondary air having a predetermined vibration frequency and maximum amplitude of oxygen concentration, and the secondary air control valve sets the vibration frequency to greater than 0 Hz and not greater than 1.5 Hz when the maximum amplitude of the oxygen concentration of the secondary air is set to a fixed value greater than 0% and not greater than 3.0%. An exhaust gas purification device characterized by:

8. The exhaust gas purification device according to claim 7, The secondary air control valve sets the frequency of the secondary air to 0.20 Hz or more and 0.94 Hz or less, or 1.2 Hz or more and 1.5 Hz or less. An exhaust gas purification device characterized by:

9. The exhaust gas purification device according to claim 7, The secondary air control valve controls the frequency of the secondary air to be greater than 0.25 Hz and less than 0.82 Hz. An exhaust gas purification device characterized by:

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